In the forthcoming evolution of the mobile cellular standards like GSM and WCDMA, new transmission techniques like OFDM is likely to occur. Furthermore, in order to have a smooth migration from existing cellular systems to the new high capacity high data rate system in existing radio spectrum, the new system has to be able to operate in a flexible bandwidth and also in frequency division duplex (FDD) and time division duplex (TDD) mode. A proposal for such a new flexible cellular system is 3G Long Term Evolution (3G LTE) that can be seen as an evolution of the 3G WCDMA standard. This system will use OFDM as multiple access technique (called OFDMA) in the downlink and will be able to operate on bandwidths ranging from 1.25 MHz to 20 MHz. Furthermore, data rates up to and above 100 Mb/s will be supported for the largest bandwidth. However, not only high rate services are expected to use 3G LTE, but also low rate services like voice. Since 3G LTE is designed for packet data (TCP/IP), VoIP (Voice over Internet Protocol) will be the service carrying speech.
One important aspect of LTE and similar systems is the mobility function, hence synchronization symbols and cell search procedures is of major importance in order for User Equipment (UE), such as a cellular phone, to detect and synchronize with adjacent cells.
A known method for detecting a symbol in a radio channel comprises the steps of match filtering a received signal using the symbol and determining the peaks in the filtered signal.
The method is used in a known method to identify a cell by user equipment. In this case the user equipment is receiving a signal from a synchronization channel. The received signal is match filtered using the synchronization symbol and peaks and corresponding timing of the filtered signal are determined. The timing information determined from the matched filter is used for later cell search stages, i.e. stages that determine frame timing and cell identity.
Whilst the known method for detecting a symbol in a radio channel and method to identify a cell, and corresponding devices, functions adequately, at least in some operational scenarios, they do have a number of disadvantages.
For example, in a time division duplex scenario where two user equipments are situated physically close to each other and one of them is communicating with a base station and the other is doing initial cell search (in the first place trying to identify a synchronization symbol). The latter user equipment will not be aware of the timing and, when the first user equipment is transmitting, the interference from the first user equipment received in the latter user equipment's receiver is much larger than the down link signal from the base station.
A drawback of the known method (and corresponding device) is that this will have the effect of an erroneous symbol matching and timing detection. Standard matched filtering techniques for symbol detection such as detection of synchronization symbols, in certain operational scenarios will give risk for very bad detection performance. This will increase the initial synchronization time considerably and, in the case of cell identification, calls risk to be lost during hand-over due to slow identification of cells by user equipment performing initial cell search and which need to hand-over to a new cell.
It is an object of the present invention to provide a method for detecting a symbol and method to identify a cell, and corresponding devices, which overcome or alleviate the abovementioned drawbacks to some extent.